And His saying: "then increase him twofold in the torment," meaning: increase his torment with another torment.
Interpretation of verses from 62 to 70 of Surah Sad.
وَقَوله: ﴿فزده عذَابا ضعفا﴾ أَي: زده عَلَى عَذَابه عذَابا آخر.
تَفْسِير الْآيَات من ٦٢ وَحَتَّى ٧٠ من سُورَة ص.